It may be possible for a planet to experience a runaway greenhouse effect even if it does not receive a higher amount of solar radiation that is considered necessary to trigger the event in the first place, a study headed by Colin Goldblatt from the University of Victoria, Canada and published in the Nature Geoscience journal this week has found.

A runaway greenhouse effect is the uncontrolled heating up of a planet’s surface resulting in the rapid evaporation of its water bodies such as oceans, which get converted to steam and make the planet inhospitable. Such an effect is triggered when the solar radiation absorbed by the planet exceeds the thermal radiation given out by it. In ideal conditions, such as in the case of Earth, the absorption and radiation levels are balanced resulting in a temperate climate.

Dr. Goldblatt’s study has found that a runaway greenhouse effect can be caused, under specific conditions, even on a planet like Earth receiving normal levels of solar radiation.

According to the study, for any given planet (like Earth) there is a specified upper limit of thermal radiation that helps balance the amount of solar radiation absorbed. The study, conducted using specific computer modeling techniques which have analysed runaway greenhouse effects at different temperatures, has found that the threshold level for thermal radiation is lower than previously thought. Similarly, the solar radiation levels have been found to be higher than previous estimations.

This lower level of thermal radiation can help cause a runaway greenhouse effect easily on Earth than believed earlier, according to the study.

Comparing the findings with planets such as Venus, the study says that Venus might have experienced a runaway greenhouse effect in the past and that “Earth’s future is analogous to Venus’s past”.

But, it may happen only after a million years or more. It further adds that such an effect is unlikely to occur due to human-induced factors.

Yet another important conclusion of the study is the narrowing down of the ‘habitable zone’ of a star in the solar system. As lower thermal radiation levels can cause even a planet like Earth to support the runaway greenhouse effect, the boundaries have been drawn closer when it comes to choosing a planet that can be part of the habitable zone.

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